1. Field of the Invention
The present invention relates generally to memory devices and methods of storing and accessing data. More particularly, the invention concerns storage of data streams in a manner that establishes a systematic relationship between the data itself and points used for accessing the data, to provide independent and extremely efficient access to, and dissemination of, the stored data streams.
2. Description of Relevant Background
Consumer demand for enhanced on-site entertainment and information services is on the rise. Examples of such entertainment and information services include so-called xe2x80x9con-demandxe2x80x9d video, interactive video games, database research, xe2x80x9chome-shoppingxe2x80x9d and the like. Numerous service providers are currently eager to tap this demand, and are therefore expressing interest in schemes for providing such services to consumers.
In order to be economically practical and viable, a system offering the wide range of information-related services just described should preferably be able to (i) store very large quantities of data at an affordable cost per bit; and (ii) provide for efficient retrieval of the data with a minimal contention between users for any portion of the data.
Memory devices according to the present invention are advantageously utilized for storing information (e.g., information in digital or analog form). The types of information capable of being stored can include video and audio information (e.g., movies, video games, television and other entertainment programs), educational information and programs, scientific and other research-related database information, consumer catalog and home-shopping information, and the like, and are hereinafter referenced generically as xe2x80x9cinformationxe2x80x9d or xe2x80x9ctitlesxe2x80x9d.
Many such types of information, in order to be useful, require that the data, which together form the information, are provided in a given sequence or order. Examples include audio information, such as speech or musical compositions, visual information, such as paintings and photographs, and audio-visual information, such as movies, television shows and video games. In the case of a movie, for example, a sequential group of still pictures is connected together on a long strip of photographic film. In order to xe2x80x9cplay backxe2x80x9d the movie, the still pictures are moved past a light source in sequence and at a certain speed, and the resulting images are focused onto a screen while the audio portion of the movie is output over speakers. These resulting images will appear to the viewer to be moving. Similarly, music stored on magnetic tape can be xe2x80x9cplayed backxe2x80x9d by moving the magnetic tape serially past a playback head of a tape player.
In analogous fashion, according to more recent techniques, digitally stored data may be stored in a memory and accessed in serial fashion to obtain the same result achieved by the more traditional storage formats mentioned above. As such, an assemblage of stored digital data, if xe2x80x9cplayed backxe2x80x9d in serial fashion, can reproduce any of the above types of information. A few of the many types of mechanisms used to store digital data are introduced here just by way of example. They include shift registers, charge coupled devices (CCDs), delay lines, read-only memory (ROM) and random-access memory (RAM).
The shift register as a technology has existed for decades. FIG. 1A shows a typical shift register arrangement. As illustrated, the shift register 10 is composed of a series of D-flip-flops 11. The number of flip-flops provided is variable and depends upon the number of bits N to be stored. In operation, clock pulses input at clock input 12 cause the data at the inputs D to transfer to the outputs Q. This clocking causes data supplied bit by bit at the data input 13 to shift right by one flip-flop. After an appropriate number of clock cycles, the data is output bit by bit at the data output 14.
The shift register illustrated in FIG. 1B is another example of a register, namely a recirculating shift register manufactured by Signetics in 1972. As shown, the shift register comprises an input 20 for data, an input selector 21, a data storage selector 22 composed of logic gates, a shift register 23, a device selector 24, an output selector 25, clock inputs 26, 27, a write control 28, a read control 29, and a data output 30. In operation, the shift register is activated by inputting high signals at the device selector 24. Then, a write enable signal is input to the write control 28, while clock input 26 receives clock pulses. At the same time, the data to be stored is fed to the input 20, thereby inputting the data to be stored. When the write control 28 is changed to low, the data storage selector 22 recirculates the stored data through the shift register 23, thereby storing the data. When it is desired to output the stored data, a read signal to the read control 29 and clock pulses to the clock input 27 trigger the output selector 25 to output the data stored in the shift register at output 30. Since the output operation does not damage the recirculating data, the output operation can be performed repeatedly for the same stored data. To alter the data stored in the register, it must be over-written with new data by a write operation, as described above. The storage capacity for this type of shift register is 512 or 1024 binary digits (bits).
Prior art delay lines, such as the one shown in FIG. 1C, are composed of a silicon substrate 31, a signal input 32, several signal taps 33 spaced equally along the substrate 31, and a signal output 34. An electrical signal entering the delay line at the input 32 propagates through the substrate 31 at a fixed, predetermined velocity. While propagating, the signal passes by each of the several taps 33, which can be used to access the data. Thus, it becomes possible to delay the propagating signal a predetermined amount of time by passing it through the delay line and then selecting an appropriate tap that corresponds to the amount of desired delay. Once the propagating signal reaches the end of the substrate, it is output from the delay line at 34.
FIGS. 1D and 1E show a CCD, where FIG. 1D is a schematic circuit diagram and FIG. 1E is a structural diagram. As shown in FIG. 1D, the CCD is composed of metal oxide semiconductor field effect transistors (MOSFETs) 40 connected in series. Amplifiers 41, 42, also composed of MOSFETs, are provided on the CCD input and the CCD output, respectively. The CCD operates similarly to the shift register (see FIG. 1A) in that a signal enters the CCD at the input 41 and progresses through the CCD from MOSFET to MOSFET in accordance with clock pulses supplied at clock inputs 43 and 44. After proceeding through the series of MOSFETs 40, the signal exits the CCD at output 42. As shown in FIG. 1E, the individual MOSFETs are formed by placing metal contact layers 45 at appropriate locations on a semiconductor substrate 46.
A typical RAM is illustrated in FIG. 1F. As shown in the drawing, an array of memory cells 50 is connected to respective series of row selectors 51, column selectors 52, write amplifiers 53, and sense amplifiers 54. In a data load operation, a particular cell to be written to is selected by providing the cell""s appropriate column and row address, using the selectors 51 and 52. The data to be written to that cell is then input to the array 50 via the write amplifiers 53. Given the prior selection operation, however, the data is stored only in the selected cell. Similarly, in a data read operation, a particular cell to be read is again selected by providing appropriate column and row addresses via the selectors 51 and 52. The data is then copied out from the array 50 via the sense amplifiers 54.
FIG. 1G illustrates a typical ROM. The structure is very similar to that of the RAM just described. An array of pre-set memory cells 60 is connected to respective series of row selectors 61, column selectors 62 and sense amplifiers 63. Operation of the ROM proceeds as described with respect to the data read operation of the RAM illustrated in FIG. 1F.
The more traditional (i.e., analog) storage and playback formats suffer from drawbacks both in limitations on dissemination and in scheduling constraints. Thus, traditionally, in order to see a movie, for example, a viewer would have to attend a scheduled showing at a predetermined location. With the advent of broadcasting, the viewer was freed from the need to travel to the showing, but nonetheless was bound by the schedule imposed by the broadcaster. In more recent times, videotape technology has effectively freed the consumer even from the former restrictions on scheduling. However, this additional measure of freedom has given rise to other inconveniences. For example, the consumer must either travel to purchase or rent a particular tape, or program a recorder in order to xe2x80x9ctime-shiftxe2x80x9d viewing of a particular scheduled broadcast.
Similarly, data stored digitally in a computer memory also suffers from limitations on access and dissemination. For instance, in an Input/Output operation performed by a computer, the computer must repeatedly perform complex, multi-step operations to access, move and output the desired data in small increments. Also, output using known addressing techniques is a dedicated operation, in that it is limited to one single destination at any given time. As a result, only one end user at a time has access to the output data. Additionally, digital storage of audio-visual information has not been widely practiced, at least in part because the above limitations render it economically unfeasible.
The memory devices according to the present invention borrow from the above philosophy of outputting data in a serial and sequential manner to convey useful information, e.g., a motion picture. The data output from such a memory device can be used to produce a moving picture or the like from, essentially, sequential frames or their equivalent. Unlike the more traditional media, however, the data is stored in a cyclical, systematic arrangement. In other words, once the data is input into the memory device, the data and some appropriate point of data access will repeatedly coincide. Furthermore, according to the present invention, once the data is input into the memory device, the location of the data can be computed, e.g., by knowing the present or past location of at least some part of the data.
Also, unlike the more traditional media, access to the data is not limited to a single scheduled output. Rather, according to the invention, there can be many output ports associated with one and the same set of stored data. These plural output ports permit independent, simultaneous access to the stored data. Also, these plural output ports can be configured to allow data cloning. Thus, the present invention provides for extremely efficient and powerful methods of data access and dissemination.
It is an object of the invention to provide a particularly useful manner of storing data.
It is a further object of the invention to provide a data storage arrangement and a data retrieval arrangement that permit very efficient access to stored data, with minimal access contention.
It is yet another object of the present invention to provide a data storage arrangement and a data retrieval arrangement that allow the stored data to be disseminated widely and efficiently.
These and other objects are solved by the present invention in its various embodiments. According to one formulation, the present invention provides a method and an apparatus for storing data which:
provide data memory in a systematic, cyclical arrangement;
provide plural data portals in an arrangement defined by modular arithmetic; and
provide sequential, relative movement between the data memory and the data portals.
As a result, when one or more of the plural portals is selected, data can be input or output in a manner which is predictable, straight-forward, free of scheduling constraints, and very efficient, without contention between the separate portals.
According to another formulation of the invention, a method and apparatus are disclosed which:
provide data memory in a systematic, cyclical arrangement;
provide a systematic arrangement of plural data outputs; and
provide sequential, relative movement between the data memory and the data outputs.
Again, when one or more of the plural outputs is selected, data stored in the data memory can be tapped in a manner which is predictable, straight-forward, and very efficient, without scheduling constraints and without contention between outputs.
The memory devices of the present invention can be designed in several different ways, as long as linkage between data and portals is assured. But it is not material how such linkage is achieved. For instance, according to one design, the memory device circulates data either through or past fixed portals. According to another, the data is stored in fixed address locations and the portals are moved from address to address. These and other alternative designs will be discussed in greater detail below in the Detailed Description.
Preferred embodiments of the invention utilize semiconductor memory technology in order to implement the memory devices. Various such semiconductor solutions are described below in the section entitled xe2x80x9cSpecific Embodiments of the Inventionxe2x80x9d. Another set of embodiments, also described below, utilizes memory storage media capable of confining propagating waves in order to implement the memory devices;